The overarching goal of this proposal is to determine how bariatric surgery affects psychiatric and metabolic outcomes among patients with bipolar disorder (BD). BD patients are at increased risk of obesity and suffer increased rates of obesity-related comorbidities. They have an estimated 25 years life lost, largely due to cardiovascular disease. There is an urgent need for knowledge about how best to treat obesity and mitigate associated comorbidities among bipolar disorder patients. Bariatric surgery is the most effective treatment for morbid obesity. Although BD patients suffer disproportionately from obesity, there is virtually no published data on how bariatric surgery affects psychiatric or metabolic course in this population. We propose a retrospective cohort study to examine psychiatric and metabolic outcomes during up to 3 years follow-up among all H100,000 morbidly obese adult patients (2000 BD, 13,000 major depressive disorder, 85,000 neither affective disorder) age 18-69 in Kaiser Permanente Northern California, between 2006 and 2009. Within the cohort, 5149 patients (171 BD, 1999 major depressive disorder, 2979 neither affective disorder) underwent bariatric surgery during the study period. We propose three aims: (1) Determine if predictors of referral to bariatric surgery, and of undergoing bariatric surgery, differ by affective disorder diagnosis (BD, major depressive disorder, neither); (2) Among n=2000 morbidly obese bipolar disorder patients who meet criteria for bariatric surgery, determine if bariatric surgery affects psychiatric course (risk of psychiatric hospitalization, outpatient psychiatric utilization); and (3) Among n=5149 patients who underwent bariatric surgery (171 BD, 1999 major depression, 2979 neither affective disorder), determine if affective disorder is associated with weight loss and metabolic outcomes (diabetes, hypertension, dyslipidemia). We will employ longitudinal data representation from the counterfactual statistical framework. Multiple linear regression will be employed for linear outcomes (weight loss, number of outpatient visits), and multiple logistic regression will be employed for dichotomous outcomes. This study will be the first to present data on outcomes of bariatric surgery among bipolar disorder patients. Current, there are no BD-specific data on which to base clinic decision making in this population. As the excess mortality in BD is largely due to cardiovascular disease, this study will provide essential information to guide clinical decision making for morbidly obese BD patients and their physicians.